What is environmental DNA?
Environmental DNA (eDNA) refers to genetic material that organisms shed into their surroundings, such as water, soil, or air. This DNA comes from sources like skin cells, mucus, feces, or decaying organisms.
What are the benefits of using eDNA?
Because eDNA is a non-invasive and highly sensitive tool, it allows researchers to gather valuable data on species populations and distribution with minimal environmental disturbance. In some environments, particularly aquatic ones, visual observation of organisms can be difficult, and traditional trapping or survey methods can be labor intensive, costly and potentially invasive to the organisms that live there.
A survey using environmental DNA (eDNA) is more cost-effective than traditional survey methods because it requires fewer resources, less field time, and minimal specialized equipment. Traditional methods, such as trapping, netting, or visual identification, often involve extensive labor, travel, and expertise, making them time-consuming and expensive. In contrast, eDNA surveys only require collecting environmental samples (e.g., water, soil) and analyzing them in a lab, reducing the need for large field teams and prolonged fieldwork. Additionally, eDNA can detect multiple species from a single sample, increasing efficiency and reducing costs associated with species-specific surveys.
An eDNA survey can be extremely sensitive and capable of detecting even trace amounts of DNA from organisms that may be rare, elusive, or difficult to observe using traditional methods. This allows for early detection of invasive species or rare wildlife, even at low population densities. Finally, eDNA surveys can be species specific as it is using genetic material from the organism, which helps to eliminate much of the human error in identifying species that may phenotypically look similar.
GMCG AmeriCorps members survey for spiny water flea using traditional plankton net methods.
What DNA is targeted in these surveys?
Mitochondrial DNA (mtDNA) is commonly used in environmental DNA (eDNA) studies because of its high copy number, stability, and species-specific genetic markers. Mitochondrial DNA is present in hundreds to thousands of copies per cell, compared to just two copies of nuclear DNA. This makes it easier to detect in environmental samples, where DNA may be present in very low concentrations. Another reason is that mtDNA is more resistant to degradation than nuclear DNA. It remains detectable in water, soil, or air for longer periods, increasing the chances of successful species identification even after the DNA has been shed. Finally, genes in mtDNA, such as cytochrome oxidase I (COI), have high genetic variation between species but are conserved within a species. This allows researchers to accurately identify specific organisms while avoiding misidentification.
How is GMCG currently utilizing eDNA?
We use eDNA for both aquatic fecal tracking and for biomonitoring purposes. In our fecal tracking project, we first test for E. coli, a common bacterium in fecal material. When high E. coli is measured, we can then use genetic material to help determine the host organism of the fecal material. This is important because identifying the host animal of fecal pollution is crucial for effective mitigation strategies as different sources of contamination require different responses. Different animals will also potentially carry different pathogens, and knowing which animal the fecal matter is derived from can also help to identify responsible parties for the source of contamination.
For biomonitoring purposes, GMCG uses eDNA to both look for species of conservation interest – such as brook trout – and for invasive species, like the spiny water flea and Asian clams. This allows for identifying critical habitats and helps prioritize areas for conservation, or in cases of surveying for an invasive, early intervention and potential mitigation of the problem. Using an eDNA system helps to keep the costs of the surveys low, is non-invasive to organisms living in that habitat, and because of its sensitivity, can potentially identify invasive threats sooner.
Spiny water flea DNA detected in a water sample from an established habitat in Lake Winnipesaukee.
What other projects can be supported by eDNA use?
Lots of different things! eDNA is a powerful tool for conservation because it enables efficient, non-invasive, and highly sensitive monitoring of species and ecosystems. Other types of projects that use eDNA can be for population and biodiversity assessments, habitat and migration studies, disease surveillance, climate change impacts, environmental impact assessments, environmental law enforcement, and habitat restoration projects, to list a few!
Support for our work generously provided by the Maine Outdoor Heritage Fund (MOHF) and The Davis Foundation.
